SF6028 - Elimination of Human Pathogens on Seeds Destined for Sprout Production by Using a Novel Sanitizer

Researcher:

Dr. Keith Warriner, Dept. of Food Science, University of Guelph

Objectives:

1. To evaluate the efficacy of SDH to inactivate a range of model pathogens (E. coli 0157; Salmonella and Listeria monocytogenes) inoculated on different seed types.
   

2. To determine the mode of action and potential of SDH resistant subpopulations emerging from treated human pathogens.
   

3. To determine the efficacy of SDH to decontaminate naturally contaminated and damaged seed.

Expected Benefits:

• This work will provide a basis for Ontario to establish the safest sprout production in the world and boost the domestic/export markets for such nutritious products.

Summary of Research Results:

Sprouted seeds (e.g. bean sprouts and alfalfa) have high nutritive value, in addition to anti-cholesterol and anti-carcinogenic constituents. Although regarded as a health food, sprouted seeds have been implicated in over 33 major foodborne illness outbreaks, especially involving Salmonella, over the last 10 years. Because sprouted seeds are produced under warm humid conditions any pathogens present can reach levels of over 1 million within 24 h of initiating the sprouting process. Simply washing sprouts before consumption is not an option since pathogens, such as Salmonella, can become internalized into the inner sprout tissue in the course of sprout development. Therefore, most efforts to enhance the safety of sprouts have been focused on seed decontamination methods applied prior to the sprouting process. However, if human pathogens become located in crevices on the seed coat they can be protected from the most potent sanitizers. For example, even the currently recommended 20, 000ppm calcium hypochlorite (equivalent to concentrated bleach) treatment cannot inactive all human pathogens on seeds. Other treatments have been applied but to date none have been shown to be fully effective.

A novel sanitizer SDH (commercial name Germin-8-or) has been evaluated as an alternative seed decontamination agent. The key advantage of SDH is that it can be supplemented into the seed soak solution without causing any detrimental affects on germination or sprout development (i.e. SDH is phytocompatible). Therefore, as the seed germinates the pathogens residing in protective sites are exposed to SDH and readily inactivated. If calcium hypochlorite was applied in the same way it would not only kill the pathogens but also the seed. Strong oxidizing agents are non-discriminate and attack multiple cellular targets (membranes, proteins, DNA). However, SDH is more selective with bacterial cell inactivation being primarily caused by disruption to membrane proteins. Plants and other eukaryotic cells are more adapted to resist the oxidative action of SDH hence are stable in the presence of the sanitizer.

In the course of the project the SDH treatment was optimized and validated using seeds inoculated with a five strain cocktail of either Salmonella or E. coli O157:H7(103-104 cfu/g) . It was found that 200ppm SDH was sufficient to provide consistent decontamination of mung bean, alfalfa, cress, clover and soybean. Experiments were also performed with naturally contaminated seed derived from plants that had been inoculated with human pathogens. Again SDH treatment was able to effectively decontaminate seeds thereby producing pathogen free sprouts.

SDH was less effective at decontaminating damage seed or other seed types such as broccoli, chick peas, onion, sesame and radish. The limitation of SDH to decontaminate all seed types was shown to be due to the slow germination rate of certain seeds and/or the presence of sanitizer sequestering agents/systems.

In conclusion, the study has demonstrated that SDH is a cost-effective, practical, alternative to the currently recommended calcium hypochlorite based seed decontamination treatment. The SDH treatment is currently seeking regulatory approval and patent protection. Once secured it is anticipated that commercial trials will follow in the near future.